1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to new and improved terminal slowdown control for elevator systems.
2. Description of the Prior Art
It is necessary in elevator systems to provide a redundant, independent means for detecting an overspeed condition of an elevator car as it approaches a terminal floor. In addition to the speed monitoring function, once an overspeed condition is detected, means must be provided for safely bringing the car to a stop.
U.S. Pat. No. 3,779,346 entitled "Terminal Slowdown Control for Elevator System", which is assigned to the same assignee as the present application, discloses an improved terminal slowdown control which provides a terminal slowdown signal by interrupting a beam of electromagnetic radiation with spaced markers as the elevator car approaches a terminal floor. The magnitude of this terminal slowdown signal indicates whether or not the elevator car is decelerating properly, and if an overspeed condition is detected, this same terminal slowdown signal is substituted for the normal slowdown pattern signal to decelerate and stop the elevator car at the terminal floor. The terminal slowdown system of U.S. Pat. No. 3,779,346 eliminates the long cams and mechanical switches of the prior art, and is thus easier to install and maintain.
The independent terminal slowdown control provides a terminal slowdown signal each time a terminal floor is approached, but if the normal slowdown and stopping control is functioning properly, and the elevator car is properlyresponding thereto, the operation of the independent terminal slowdown control is not apparent.